Production methods of a layered titanate represented by a general formula AxMy□zTi2−(y+z)O4 (wherein A and M are different metals each with a valence of 1-3, □ represents a defect site of Ti, x is a positive real number and satisfies 0<x<1.0, and y and z are independently 0 or a positive real number and satisfy 0<y+z<1.0.) are described, for example, in Japanese Patent No. 2656778 and D. Groult , C. Mercy and B. Raveau, Journal of Solid State Chemistry, vol.32, p 289 (1980). According to these production methods, a layered titanate can be synthesized by calcining a mixture containing metals A and M, each in the form of its carbonate, nitrate or oxide, and titanium dioxide.
The present applicant previously discovered a production method of a layered titanate having a lamellar form, a low tendency of particle agglomeration and superior dispersibility. The method is now found in Japanese Patent No. 3062497. In accordance with this production method, a mixture is provided containing a compound which produces an oxide of a metal A when it is thermally decomposed, such as a hydroxide, carbonate or nitrate of the metal A; a compound which produces an oxide of a metal M when it is thermally decomposed, such as a hydroxide, carbonate or nitrate of the metal M; and a titanium dioxide or a titanium compound which when thermally decomposed produces titanium dioxide. Then, a flux such as a chloride or sulfate of an alkaline metal or alkaline earth metal is added to the mixture which is subsequently calcined.
The layered titanate is ion exchangeable and has the property of swelling when a basic compound is inserted between its layers, like bentonite and swelling mica. International Patent Publication No. WO 99/11574 describes a method for preparation of lamellar titania by mixing titania and an amine or ammonium compound, stirring the mixture to thereby provide a sol of lamellar titania delaminated to a single or plural layers, spray drying the lamellar titania sol to provide fine hollow particles and then grinding the fine hollow particles.
Lamellar mica and talc are used as fillers for paints and resins, cosmetic materials and pigments. The layered titanate produced by the method described in Japanese Patent No. 3062497 also has a well-dispersible lamellar form, but exhibits a smaller particle diameter/thickness ratio, compared to high-quality mica. The higher particle diameter/thickness ratio is accordingly required for the layered titanate.
A dispersing method known to be useful for delamination of the layered titanate is disclosed in International Patent Publication No. WO 99/11574.
In the method described in the above-cited International Publication, freeze drying or spray drying is required to prevent relamination or reagglomeration of the lamellar titania sol and improve dispersibility. Such freeze drying or spray drying requires special equipment, reduces productivity and increases energy consumption, which have been problems.